This invention relates to electromagnetically operated slit shutters.
Conventionally, shutters for controlling the exposure of photographic material in cameras have made use of drive mechanisms which are powered by mechanical biasing means such as springs to drive the shutter blades (or shutter curtains) in one direction. Such conventional type shutter drive mechanisms necessitate the provision of cocking means arranged after the termination of exposure to return the shutter blades to the initial position while tensioning the springs, thus preparing for the next exposure. The addition of the resetting mechanism makes the entire system complicated and increases the necessary number of constituent parts with the disadvantage that as the scale and complexity of the equipment for assembling and production is increased, it becomes difficult to achieve a minimization of the production cost.
To eliminate the above-described problems of the spring-powered shutter drive mechanism and, moreover, to obtain a shutter of higher accuracy and better quality than those of the above-described shutter, it has been proposed to make use of an electrically operated magnetic control device in controlling the opening and closing movement of the shutter blades.
The arrangements to these devices may be classified into the following three main groups:
(1) A mechanism wherein a coil or other suitable conductor is arranged in the magnetic field of a permanent magnet which, upon passage of current therethrough, causes the coil to move, thus providing a so-called moving coil type drive control mechanism.
(2) A mechanism wherein a magnetic member such as an iron rod is arranged in a space within a coil or other suitable conductor so that upon passage of current through the coil this member is moved as the magnetic resistance is changed, thus providing a so-called plunger type drive control mechanism.
(3) A mechanism wherein a permanent magnet and a plurality of coils constitute a linear motor type drive control mechanism.
The above-described three arrangements have a common feature that either the coil, or the iron plunger is driven to move, and this motion is transmitted to the shutter blades through a linkage or the like. Therefore, the sum of the weights of the coil or iron plunger, the linkage and other associated moving parts becomes heavier than that of the weights of the moving parts of the spring-powered shutter drive mechanism, so that when the shutter is released, it tends to strike on the stop member thereby causing of a shock of significant magnitude, which shock causes vibrations in the camera.
Another disadvantage is that since the mating pattern of the relatively heavy coil or iron plunger with the shutter blades is improper, the conventional mechanism is susceptible to the influence of gravity (gravitational pulling effect) and the shutter speed setting is apt to change its value by a magnitude depending upon the attitude of the camera.
The present invention has for its general object to provide an electromagnetically operated shutter in which an significantly reduced force is sufficient for driving the shutter blades, whereby the magnitude of shock resulting from the stoppage of the running down shutter blade is minimized to prevent introduction of vibrations to the camera.
To achieve this, according to the present invention, the shutter blades and the moving parts of the electrically operated magnetic control device are drivingly connected to each other by pivoted members, and the arrangement of these parts is such that each shutter blade and the moving part of the drive means therefor are moved in opposite directions to each other in symmetry with respect to the axis of the rotating link member.
This arrangement enables the shutter blades and drive means to be balanced in weight by the link members in all stations of movement thereof, thus making it possible to control the movement of the shutter blades with relatively smaller power requirements, and to significantly improve the reliability of the shutter speed control which would be otherwise dependent upon the attitude of the camera.
The present invention will next be described in greater detail in connection with embodiments thereof by reference to the drawings.